1. Field of the Invention
The invention relates to motorized drives for sewing machines, and in particular to motors in association with belts for use in driving the operating mechanism of sewing machines.
2. Description of the Prior Art
It is common practice to have a motor drive an arm shaft in the bracket arm of a sewing machine through a timing belt that runs over a small diameter pulley on the motor shaft and a larger diameter speed reducing pulley on the arm shaft; and further to have the arm shaft drive a hook shaft in the bed of the machine through another timing belt. It is also well known to have the motor in a frame which can be pivotally adjusted in the machine to tighten the belt between the motor and arm shaft, and to have the other belt run over one or more idlers which can be positionally adjusted to tighten such other belt. There are however, a number of disadvantages to the use of a motorized drive as described in a sewing machine.
Among the disadvantages of the described system is the need to provide separate belt tensioning means for each of two belts which must be adjusted to a desired degree of tightness. Disadvantages also arise from the use of idlers since they add to the cost of a system, generate heat and increase the inertia of the system. Furthermore, the described system is unsuited to the use of a high speed motor because the required speed reduction is not then obtainable at the arm shaft with a pulley of convenient size. A relatively low speed motor, which is therefor inefficient and a source of considerable heat, must be used. As a consequence the frame supporting the motor for pivotal movement in the machine must be fashioned from metal to conduct heat away from the motor rather than from a non-conducting, less expensive plastic material. In addition, the use of two rather long belts introduces lost motion into the system.
The said disadvantages are eliminated in accordance with the invention, with an improved modular motorized drive and novel means for mounting the drive in a sewing machine.